1. Field of the Invention
The present general inventive concept relates to an image encoding/decoding technique, and more particularly, to a method of encoding/decoding an omni-directional image for three-dimensional (3D) realistic broadcasting.
2. Description of the Related Art
Omni-directional video camera systems are camera systems that photograph a 360° omni-directional view from a single viewpoint. Omni-directional video camera systems include a camera to which a special mirror, such as a hyperboloid mirror, or a special lens, such as a fish-eye lens, is installed or a plurality of cameras to photograph an omni-directional view. Studies on omni-directional video encoding for adapting video information generated by such an omni-directional video camera system to be broadcast are in progress.
An example of using omni-directional video encoding is 3D realistic broadcasting. For example, all image information regarding scenes viewed from diverse viewpoints including a viewpoint of a pitcher, a viewpoint of a catcher, a viewpoint of a hitter, and a viewpoint of an audience on the first base side in a baseball game is provided to a viewer's terminal. The viewer can select a desired viewpoint and view a scene from the desired viewpoint.
Quick Time VR® is an example of 3D realistic broadcasting. According to the Quick Time VR®, photos with a 360° cylindrical or cubical panoramic view can be produced and rotated 360° or zoomed in. However, users must download information regarding all panoramic images in advance of viewing the images, and the quality of these images is very low.
Studies on a technique of applying conventional two-dimensional (2D) image encoding methods, such as Motion Picture Experts Group (MPEG)-4 and H.264, to omni-directional 3D images are in progress. FIG. 1 is a conceptual diagram of a conventional omni-directional video encoding/decoding system. Referring to FIG. 1, an omni-directional image is acquired using an omni-directional photographing unit 110. An image converter 120 converts the omni-directional image into a predetermined format that can be processed by an existing MPEG-4 encoder 130.
An image photographed using an omni-directional camera system using a special lens or mirror or a plurality of cameras has characteristics corresponding to a 3D spherical environment. Since a conventional video codec receives, compresses, and transmits a 2D image, a 3D image photographed using an omni-directional camera system needs to be converted into a 2D image. Cartographical projection and polygonal projection have been presented to convert a 3D image into a 2D image.
Cartographical projection is a process of projecting a spherical shape onto a complete rectangular plane like producing a typical world map. Polygonal projection is a process of projecting a spherical shape into a development figure of a polyhedron.
The MPEG-4 encoder 130 encodes the converted image to generate a bitstream and transmits the bitstream to a decoding unit of a user. An MPEG-4 decoder 140 decodes the bitstream. An image converter 150 converts the decoded bitstream into an omni-directional image. A display unit 160 displays the omni-directional image.
Since the amount of omni-directional image data to be transmitted to a user is large, a very broad bandwidth is needed to transmit the omni-directional image data to the user in real time. Moreover, problems like transmission delay and limits in performance of a user's decoding unit may occur. Furthermore, when conventional 2D image encoding is applied to an omni-directional image as it is, regardless of characteristic differences between an omni-directional image and a 2D image, encoding efficiency decreases.